Energy-based tissue welding has previously been used with laser, ultrasonic, radio-frequency (RF) energy, or direct thermal cautery technologies. RF tissue welding and other energy based technologies are commercially available to seal and ligate small blood vessels. Some examples include the LigaSure™ ligation device manufactured by Covidien of Mansfield, Mass., the EnSeal® ligation device manufactured by SurgRx® of Redwood City, Calif., the PKS Seal™ device manufactured by Gyrus Group PLC (Olympus of Toyko, Japan) and the Starion™ ligation device manufactured by Starion Instruments of Sunnyvale, Calif. While these devices are indicated solely for vessel ligation, surgeons have attempted to use available vessel sealing technology to weld large tissue structures such as lung and bowel in thoracic and general surgery.
The primary limitation of adapting currently available vessel sealing technology to large tissue structures is marginal or insufficient weld strength. With current vessel sealing technology, RF energy is directed into the target tissue, which in turn is heated at that location. Electrical current, voltage and power may be adjusted using a closed-loop control algorithm based on feedback variables (e.g., impedance, time, temperature, phase, current, power, and voltage, etc.). The mechanism of fusing tissue in opposite layers relies on collagen and elastin protein denaturation in combination with tissue compression to create a physical entanglement of protein chains. The effected tissue is thermally damaged and non-viable. The acute inflammatory response to the thermal injury is minimal, and the proliferative phase (i.e., fibroblast and collagen deposition) of wound healing is believed to last between 2 to 4 weeks, although strength of the effected tissue can be comparative to native tissue in as little as 7 days.
A significant advantage of RF-energy tissue sealers is the ability to reduce the overall device size as compared to larger mechanical suture devices due to design flexibility with wiring and electrodes. This further enables minimally invasive surgery. The necessity of a smaller endoscopic device has led a number of surgeons to use currently available RF vessel sealing technology on pediatric lung resection and on selected complicated thoracic procedures in adults. (See, for example, Albanese C T, Rothenberg S S. Experience with 144 consecutive pediatric thoracoscopic lobectomies. J Laparoendosc Adv Surg Tech A. 2007 Jun.; 17(3):339-41. PMID: 17570785; Rothenberg, S. S., Thoracoscopy in infants and children: the state of the art. J Pediatr Surg. 2005 Feb.; 40(2):303-6. PMID: 15750919; Shigemura N, Akashi A, Nakagiri T. New operative method for a giant bulla: sutureless and stapleless thoracoscopic surgery using the Ligasure system. Eur J Cardiothorac Surg. 2002 October; 22(4):646-8. PMID: 12297194; Shigemura N, Akashi A, Nakagiri T, Ohta M, Matsuda H. A new tissue-sealing technique using the Ligasure system for nonanatomical pulmonary resection: preliminary results of sutureless and stapleless thoracoscopic surgery. Ann Thorac Surg. 2004 Apr.; 77(4):1415-8; discussion 1419. PMID: 15063276; Tirabassi M V, Banever G T, Tashjian D B, Moriarty K P. Quantitation of lung sealing in the survival swine model. J Pediatr Surg. 2004 March; 39(3):387-90. PMID: 15017557)
For smaller sections, weld strengths on pulmonary tissue are satisfactory and comparable to conventional methods (e.g., surgical staplers). In a study conducted by Tirabassi et al., lung biopsy sites were created with RF energy (using the Ligasure™ ligation device) or an endoscopic stapler (using the Endo-GIA stapler device.) Both biopsy sites had burst strengths equal to or greater than normal lung tissue in the swine survival model after 7 days (84 cm H2O and 88 cm H2O, respectively.) The wedge biopsy sections had respective average sizes of 0.87 g and 0.78 g. In studies on larger pulmonary resections (e.g., greater than 1.5 grams), the RF vessel sealing weld strength is reduced significantly as demonstrated by Santini et al. (see Table 1).
TABLE 1Resistance of RF-based wedge resection margins in porcine lungs tothe critical pressure of 82 cm H2O (60 mm Hg) [SANTINI et al.]Percentage of RF-based welds with burstsResection sizeabove critical pressure(grams)950.2950.4900.6900.8801.0851.2681.4
Despite the adoption in pediatric thoracic surgery, RF-based tissue welding is generally not used for larger resections, limiting practical use in typical thoracoscopic procedures on adults. Stapling continues to be used for most lung resections. Despite its obvious drawbacks related to size, rigidity, associated complications, and cost, stapling allows simultaneous clamping, severance and closure in adults. However, it may be desirable to increase weld strength and leak resistance in larger resections by reinforcing the weld with a bioabsorbable polymer. Bioabsorbable polymers are currently being used, or investigated for use, in wound closure, scaffolds for tissue engineering, drug delivery systems, cardiovascular, orthopedic, dental, intestinal surgeries, and cosmetic dermatology.
Energy-based tissue welding is currently on the forefront of enabling minimally invasive surgery. Some users have exceeded the limits of existing RF vessel sealing technology for certain types of surgeries. Significant improvements in weld strength may allow larger resections, and may potentially eliminate the need for surgical staples altogether.